Friction clamping apparatus

ABSTRACT

A friction clamping apparatus includes: a rod; a plurality of friction clamping units serially connected in the axial direction of the rod, each of the friction clamping units including a radially elastically transformable sleeve and a ram into which the sleeve is fittingly inserted, the rod being fittingly inserted through the respective sleeves of the friction clamping units; and restraint pressure chambers defined by an inner circumferential surfaces of the ram and outer circumferential surfaces of the sleeve respectively, so that an oil pressure is made to act upon the restraint pressure chambers to restrain the rod with the sleeves or the oil pressure is made so as not to act upon the restraint pressure chambers to release the rod from the sleeves.

BACKGROUND OF THE INVENTION

The present invention relates to a friction clamping apparatus.

As a conventional friction clamping apparatus, known is that shown inFIG. 4, in which a sleeve 01 having a collar portion 02 is fittinglyinserted through an outer cylinder 03 so that the collar portion 02 isengaged with one end surface of the outer cylinder 03 to thereby form arestraint pressure chamber between the outer cylinder 03 and the outercircumferential surface of a small diameter portion of the sleeve 01,and a shaft 07 is slidably fittingly inserted through the hole of thesleeve 01. A pressurized fluid is supplied into the restraint pressurechamber through a leading hole 05 so as to reduce the diameter of thesleeve 01 to urge the sleeve 01 against the outer circumferentialsurface of the shaft 07 to thereby produce a friction force between thesleeve 01 and the shaft 07 to restrain the shaft.

In such a conventional apparatus, the sleeve receives a reaction forceagainst a force F, given to the shaft at the time of restraintconcentrically in the vicinity of the collar portion of the sleeve, sothat it is necessary to make the sleeve thick enough to have strengthagainst the reaction force. As a result, not only has there been aproblem that the apparatus becomes large in size, but, in the worstcase, there has been a problem that it is difficult to performprocessing and assembling from the standpoint of accuracy in processingand assembling and also difficult to perform maintenance and inspection.There has been a further problem that the pressure for a pressurizedfluid required for shrinking a sleeve becomes large.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to solve theforegoing problems in the prior art.

It is another object of the present invention to provide a frictionclamping apparatus in which the thickness of the sleeve can be madethinner than a conventional one, and the pressure for a pressurizedfluid required for shrinking the sleeve can be set to a lower value.

In order to attain the above objects, according to an aspect of thepresent invention, the friction clamping apparatus comprises: a rod; aplurality of friction clamping units serially connected in the axialdirection of the rod, each of the friction clamping units including aradially elastically transformable sleeve and a ram into which thesleeve is fittingly inserted, the rod being fittingly inserted throughthe respective sleeves of the friction clamping units; and restraintpressure chambers defined by an inner circumference of the outercylinder and an outer circumference of the sleeve respectively, so thatan oil pressure is made to act upon the restraint pressure chambers torestrain the rod with the sleeves and the oil pressure is made so as notto act upon the restraint pressure chambers to release the rod from thesleeves.

According to another aspect of the present invention, the frictionclamping apparatus comprises: a plurality of clamping units, each of theclamping units including a radially elastically transformable sleeveprovided with a collar portion and outer cylinder, the sleeve beingfittingly inserted into the outer cylinder so that the color portionengages air-tightly with one end surface of the cylinder to therebydefine a restraint pressure chamber by an inner circumference of theouter cylinder and an outer circumference of the sleeve, the clampingunits being different in axial length from each other; and a rodslidably fittingly inserted through the respective sleeves of theplurality of clamping units.

According to a further aspect of the present invention, the frictionclamping molding apparatus comprises: a rod; a friction clamping portionincluding a series of a plurality of sleeves, a series of a plurality oframs, one of the rams being fittingly inserted into an adjacent one ofthe rams so that the rams are connected in series one by one, the rodbeing fittingly inserted through the series of sleeves, the series ofsleeves being fittingly inserted into the series of rams respectively soas to form oil chambers between the sleeve and the rams respectively sothat an oil pressure is made to act upon the oil chambers to therebyrestrain the rod and the sleeves with each other; and a clamping portionincluding a housing, the rod being fittingly inserted through thehousing, the outermost one of the rams being fittingly inserted into thehousing so as to form an oil clamping chamber so that an oil pressure ismade to act upon the oil clamping chamber to thereby generate a clampingforce.

In the first and second aspects of the present invention, the oilchambers of the friction clamping portion are operated by oil pressurethrough oil paths to thereby transform the sleeves elastically so as togenerate a friction force between the rod and the sleeves so that therod and the sleeves are restrained with each other. In such a state, inthe case where the oil chamber and the oil path are formed between thelower end portion of the rams of the friction clamping portion and thehousing, the oil chamber is operated by oil pressure through the oilpath so that it is possible to produce a clamping force. On the otherhand, if the oil pressure given to the oil chambers is released throughthe oil paths, it is possible to release the state of restraint with therod.

In the third aspect of the present invention, in the state where apressurized fluid has not been supplied to the restraint pressure foreach clamping unit, the sleeves fittingly inserted into the outercylinders can slide along the rod, so that respective clamping units areguided by the rod slidably in the axial direction.

On the other hand, if a pressurized fluid is supplied to the restraintchambers of the respective clamping units, the sleeves are shrunk in theradial direction by the pressure of the pressurized fluid, so that theinner circumferential surfaces of the respective sleeves are pressedagainst the outer circumferential surface of the rod respectively tothereby produce a friction force and the respective sleeves and the rodare restrained to be integrated with each other. At the time of thisrestraint, the reaction force against the force given to the rod isdispersed to the respective clamping units. As a result, in therespective clamping units, their sleeves are expanded in the axialdirection and at the same time their outer cylinders are shrunk in theaxial direction so as to be transformed.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will be apparentfrom the following description taken in connection with the accompanyingdrawings, wherein:

FIG. 1 is a sectional view illustrating a main part of an embodiment ofthe friction clamping apparatus according to the present invention;

FIG. 2 is a sectional view illustrating a main part of anotherembodiment of the friction clamping apparatus according to the presentinvention;

FIG. 3 is a sectional view illustrating a main part of a furtherembodiment of the friction clamping apparatus according to the presentinvention; and

FIG. 4 is a sectional view illustrating a main part of a conventionalfriction clamping apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the drawings.

FIG. 1 shows a first embodiment of the present invention.

In FIG. 1, a friction clamping portion provided with a cylindrical rod 1fittingly inserted through sleeves 2 and 3 can slide in the axialdirection if an external force is not given thereto. The sleeves 2 and 3are fittingly inserted through rams 4 and 5 respectively, and the rams 4and 5 are connected to each other by connection members 14 such asbolts.

The rams 4 and 5 have large-diameter portions formed on the insidethereof respectively so as to form annular oil chambers 6 and 7 betweenthe sleeves 2 and 3 and the rams 4 and 5 respectively. The axially upperand lower end portions of the oil chambers 6 and 7 are sealed by sealmembers 8 through 11 respectively. Oil pressure can be supplied to orreleased from the oil chambers 6 and 7 through oil paths 12 and 13respectively.

Next the operation of this embodiment will be described. When oilpressure is applied to the oil chambers 6 and 7 of the friction clampingportion through the oil paths 12 and 13, the sleeves 2 and 3 aretransformed elastically to thereby produce a friction force between therod 1 and each of the sleeves 2 and 3, so that the sleeves 2 and 3 arerestrained with the rod 1. In such a state of fixation, when anotherexternal force is applied to the sleeves 2 and 3 or the rams 4 and 5, itis possible to hold the external force in the rod 1, so that thismechanism may be used as a clamping apparatus. On the other hand, if theoil pressure having been given to the oil chambers 6 and 7 is releasedthrough the oil paths 12 and 13, the state of restraint with the rod 1can be released. When the state of restraint of the sleeves 2 and 3 withthe rod 1 is released in this manner, the sleeves 2 and 3 become movableon the rod 1.

In the above embodiment, although the restraint portion is constitutedby two pairs of sleeves and rams, three or more pairs of sleeves andrams may be used in accordance with a necessary friction force.

The oil for supplying pressure to the oil chambers 6 and 7 may bereplaced by any other medium.

FIG. 2 shows a second embodiment according to the present invention. Inthis embodiment, as shown in FIG. 2, a ram 5 is fittingly inserted intoa ram 4. The combination portion of the rams 4 and 5 is sealed by a sealmember 19. In this restraint portion, a rod 1 of the friction clampingportion is fittingly inserted through a housing 14 so as to form an oilchamber 15 defined by the rams 4 and 5 of the friction clamping portionand the housing 14. In the oil chamber 15, the combination portion ofthe housing 14 and the rams 4 and 5 is sealed by seal members 17 and 18respectively. Oil pressure can be supplied to or released from the oilchamber 15 through an oil path 16. The other parts are arranged in thesame manner as those in the first embodiment.

Next the operation of the second embodiment will be described. In thisembodiment, in the state of restraint of the sleeves 2 and 3 with therod 1, if oil pressure is supplied, through the oil path 16, into theoil chamber defined by the respective lower end portions of the rams 4and 5 of the friction clamping portion and the housing 14, the housing14 is urged to move downwards in the drawing of FIG. 2, so that it ispossible to produce a restraint force. The reaction force thereof actsonto the sleeves 2 and 3 through the rams 4 and 5, but the pressurereceiving areas of the rams 4 and 5 are shared equally or suitably, sothat equally or suitably shared reaction force acts onto the sleeves 2and 3. The other operation is the same as that in the first embodiment.

In the same manner as in the first embodiment, if necessary, three ormore pairs of sleeves and rams may be serially combined. The pressuredoil supplied to the oil chambers 6 and 7 may be replaced by any othermedium. Although the sleeve 2 and the ram 4 and the sleeve 2 and the ram5 are connected with each other separately by bolts, they may beconnected with each other by means of a single bolt.

Next, a third embodiment of the present invention will be described withreference to FIG. 3.

As shown in FIG. 3, three clamping units 38a, 38b and 38c having anarrangement which will be described later and having different lengthsare mounted on a shaft 39 in the order of increasing length from theillustrated upper portion.

The configuration of each of the clamping units 38a, 38b and 38c will bedescribed.

Elastically transformable sleeves 31a, 31b and 31c having collarportions 32a, 32b and 32c respectively are fittingly inserted into outercylinders 33a, 33b and 33c air-tightly so as to make the collar portions32a, 32b and 32c engage with one-side ends of the outer cylinders 33a,33b and 33c respectively, so that restraint pressure chambers 34a, 34band 34c are formed by concave portions respectively formed in the innercircumferential surfaces of the respective outer cylinders 33a, 33b and33c and the outer circumferential surfaces of the respective sleeves31a, 31b and 31c respectively. The restraint pressure chambers 34a, 34band 34c are provided with leading holes 35a, 35b and 35c respectively sothat a pressurized fluid can be supplied into the restraint pressurechambers 34a, 34b and 34c from a not shown pressed-fluid producingsource through the respective leading holes 35a, 35b and 35c. Thereference numeral 36 represents a seal constituted by an O-ring, or thelike, for maintaining air- tightness so as to prevent the pressurizedfluid from leaking out of the restraint pressure chambers 34a, 34b and34c.

A hole 37a is formed in the end surface of the outer cylinder 33a whichcontacts with the clamping unit 38b illustrated in the center and whichbelongs to the short clamping unit 38a illustrated in the uppermostposition in the drawing and positioned oppositely to the collar portion32b of the sleeve 31b of the center clamping unit 38b, and the collarportion 32b of the sleeve 31b of the center clamping unit 38b isfittingly inserted into the hole 37a so as to provide a space betweenthe end surface of the collar portion 32b and the bottom surface of thehole 37a. In the same manner, a hole 37b is formed in the end surface ofthe outer cylinder 33b which contacts with the long clamping unit 38cillustrated in the lowermost position in the drawing and which belongsto the center clamping unit 38b opposite to the collar portion 32c ofthe sleeve 31c of the lower clamping unit 38c, and the collar portion32c of the sleeve 31c of the lower clamping unit 38c is fittinglyinserted into the hole 37b so as to provide a space between the endsurface of the collar portion 32c and the bottom surface of the hole37b.

The above-mentioned spaces are for the purpose to absorb thetransformation of the respective clamping units 38a, 38b and 38c causedby giving the clamping units 38a, 38b and 38c reaction force indicatedby the arrow f against a force indicated by the arrow F which is givento the shaft 39 at the time of restraint as shown in FIG. 3. That is, bythe above-mentioned reaction p force f, the sleeves 31a, 31b and 31c areexpanded in the same direction as the force of the arrow F, while theouter cylinders 33a, 33b and 33c are compressed and shrunk in the axialdirection.

Describing more in detail, since the sleeve 31a of the upper clampingunit 38a is expanded and the outer cylinder 33a is shrunk, indeed thecounter-collar-portion-side top end portion of the sleeve 31a projectsover the hole 37a toward the illustrated lower, but as mentioned above,because of providing a space between the top end surface of the collarportion 32b of the sleeve 31b of the center clamping unit 38b and thehole 37a, the expansion of the sleeve 31a and the shrinkage of the outercylinder 33a are absorbed. In the same manner, the transformation of thecenter clamping unit 38b, that is, the expansion of the sleeve 31b ofthe center clamping unit 38b and the shrinkage of the outer cylinder 33bare absorbed by a space between the end surface of the collar portion32c of the sleeve 31c of the lower clamping unit 38c and the bottomsurface of the hole 37b.

Next, the operation of this embodiment will be described.

In order to restrain each of the clamping units 38a, 38b and 38c, thatis, in order to restrain each of the sleeves 31a, 31b and 31c with theshaft 39, a pressurized fluid is supplied to the restraint pressurechambers 34a, 34b and 34c through the leading holes 35a, 35b and 35crespectively at the same time. By the pressure of the pressurized fluidsupplied to the respective restraint pressure chambers 34a, 34b and 34c,the sleeves 31a, 31b and 31c are shrunk in the radial direction andpressed against the shaft 39 to thereby generate friction forces betweenthe outer circumferential surface of the shaft 39 and the innercircumferential surfaces of the sleeves 31a, 31b and 31c respectively,so that the sleeves 31a, 31b and 31c are restrained so as to beintegrated with the shaft 39. The sleeves 31a, 31b and 31c and therespective outer cylinder 33a, 33b and 33c are, as mentioned above,restricted in the axial direction by their collar portions 32a, 32b and32c and the end surfaces of the respective cylinders 33 a, 33b and 33c,so that the outer cylinders 33a, 33b and 33c are integrated with theshaft 39 through the respective sleeves 31a, 31b and 31c.

At the time of the above-mentioned restraint, assume that the quantitiesof expansion of the respective sleeves 31a, 31b and 31c, at the time ofgiving the force of the arrow F to the shaft 39, are S1, S2 and S3, andthe quantities of shrinkage of the respective outer cylinders 33a, 33band 33c are r1, r2 and r3. In order to make description simple, assumethat the shaft 39 is a perfect rigid body. Assuming that the frictionforces produced on the respective clamping units 38a, 38b and 38c aref1, f2, f3, then the total friction force fs is expressed by:

    fs=f1+f2+f3                                                (1)

Then, the quantity of expansion S1 of the upper sleeve 31a and thequantity of shrinkage r1 of its outer cylinder 33a are caused by thefriction force f1 of the upper clamping unit 38a, and in the samemanner, S2 and r2 are caused by the friction force f2 of the centerclamping unit 38b, and S3 and r3 are caused by the friction force f3 ofthe lower clamping unit 38c.

Therefore, if the lengths of the respective sleeves 31a, 31b and 31c ofthe respective clamping units 38a, 38b and 38c and their outer cylinders33a, 33b and 33c are established so that (S3-r2)=S2 and (S2-r1)=S1, thereaction force against the force of the arrow F given to the shaft 39can be dispersed to the clamping units 38a, 38b and 38c.

In the above-mentioned embodiment, although three clamping units areprovided, the number of clamping units may be two or not less than four.In addition, the order of overlaying clamping units is not limited inthe above-mentioned embodiment, the order of overlaying may be reversed,or may be set desiredly.

Since the present invention has such configurations as described above,it is possible to obtain the following effects.

That is, by combining a plurality of sleeves and rams as shown in thefirst and second embodiment, it is possible to make individual partscompact so that it is easy to process and assemble the parts, and if alarge friction force is necessary, it is possible to use the apparatuswithout limitation by increasing the number of combined pairs.

In addition, in the case where a plurality of pairs of sleeves and ramsare combined, by controlling oil pressure given to spaces formed by therespective sleeves and rams separately, in combination with the formereffect, it is possible to give a number of degrees of freedom to afriction force in a wide range from a small friction force to a largefriction force.

In addition, as shown in the third embodiment, since a load in the axialdirection is dispersed to a plurality of sleeves, it is possible to makethe thickness of sleeves thinner than conventional ones, so that it ispossible to establish the pressure of a pressurized fluid required forshrinking the sleeves in the diameter direction to a low value. Inaddition, in the case of establishing the pressure to the same asconventional one, contact pressure per unit area of the sleeve innercircumferential surface with the rod outer circumferential surfacebecomes large, so that it is possible to obtain a large friction forcein a comparatively small contact area and it is possible to make theapparatus small in size.

In addition, in the case of producing a large friction clampingapparatus, since the lengths of individual sleeves and outer cylindersare comparatively short, it is possible to improve the processingaccuracy, and it is possible to reduce the processing cost.

What is claimed is:
 1. A friction clamping apparatus adapted for usewith a rod, comprising:a plurality of friction clamping units seriallyconnected in the axial direction of said rod, each of said frictionclamping units including a radially elastically transformable sleeve anda ram into which said sleeve is fittingly inserted, said rod beingfittingly inserted through the respective sleeves of said frictionclamping units, wherein a ram of a first friction clamping unit of saidplurality of friction clamping units is connected to a ram of a secondfriction clamping unit of said plurality of friction clamping units; aplurality of restraint pressure chambers defined by innercircumferential surfaces of respective rams of said plurality offriction clamping units and outer circumferential surfaces of respectivesleeves of said plurality of friction clamping units, so that either afluid pressure is made to act upon said restraint pressure chambers ofsaid plurality of friction clamping units to restrain said rod with saidsleeves or the fluid pressure is made so as not to act upon saidrestraint pressure chambers of said plurality of fiction clamping unitsto release said rod from said sleeves; a restraint portion including ahousing into which said rod and said ram of the outermost-end one ofsaid plurality of friction clamping units are fitted; and a clampingfluid pressure chamber formed between said housing and a lower portionof said ram of said outermost-end friction clamping unit, so that afluid pressure is made to act upon said clamping fluid pressure chamberto generate a clamping force.
 2. A friction clamping apparatus adaptedfor use with a rod, comprising:a plurality of friction clamping unitsserially connected in the axial direction of said rod, each of saidfriction clamping units including a radially elastically transformablesleeve and a ram into which said sleeve is fittingly inserted, said rodbeing fittingly inserted through the respective sleeves of said frictionclamping units; a plurality of restraint pressure chambers defined byinner circumferential surfaces of respective rams of said plurality offriction clamping units and outer circumferential surfaces of respectivesleeves of said plurality of friction clamping units, respectively, sothat a fluid pressure is made to act upon the restraint pressurechambers of said plurality of friction clamping units to restrain saidrod with said sleeves or the fluid pressure is made so as not to actupon said restraint pressure chambers of said plurality of frictionclamping units to release said rod from said sleeves; and a restraintportion, said restraint portion including a housing into which said rodand said ram of the outermost-end one of said plurality of frictionclamping units are fitted, and a clamping fluid pressure chamber formedbetween said housing and a lower portion of said ram of saidoutermost-end friction clamping unit, so that a fluid pressure is madeto act upon said clamping fluid pressure chamber to generate a clampingforce, wherein the ram of one of said friction clamping units isfittingly inserted into the ram of a second adjacent one of saidplurality of friction clamping units so as to form a set of rams, saidrams in sets being connected in series.
 3. A friction clamping apparatusaccording to claim 2, wherein said fluid is oil.
 4. A friction clampingapparatus adapted for use with a rod, comprising:a friction clampingportion including a plurality of sleeves in a series arrangement, aplurality of rams in a series arrangement, one of said rams beingfittingly inserted into an adjacent one of said rams so that said ramsare connected in series one by one, said rod being fittingly insertedthrough said series of sleeves, said series of sleeves being fittinglyinserted into said series of rams respectively to form fluid chambersbetween said sleeve and said rams respectively so that a fluid pressureis made to act upon said fluid chambers to thereby restrain said rod andsaid sleeves with each other; and a clamping portion including ahousing, said rod being fittingly inserted through said housing, theoutermost one of said rams being fittingly inserted into said housing toform a fluid clamping chamber so that a fluid pressure is made to actupon said fluid clamping chamber to thereby generate a clamping force.5. A friction clamping apparatus according to claim 4, wherein saidfluid is oil.